Oxo-bridged binuclear iron centers are probably ubiquitous in living systems. To date, they have been specifically identified at the active sites of invertebrate hemerythrins and myohemerythrins, ribonucleotide reductase from Escherichia coli, a purple acid phosphatase from beef spleen, and in porcine uteroferrin. The bovine purple acid phosphatase is a rather unselective enzyme which dephosphorylates phosphoproteins and may regulate protein synthesis or metabolism. Uteroferrin shows phosphatase behavior and may also serve to transport iron into the fetus. Ribonucleotide reductases catalyze the reduction of ribonucleotides to the corrsponding deoxyribonucleotides. They regulate DNA synthesis and are thus central to life. Hemerythrin and myohemerythrin are the oxygen transport and storage pigments found in a number of marine organisms. At present, far more is known about hemerythrin than any of the other systems but much remains recondite. Increased knowledge of these important yet apparently unrelated biochemical systems, could come from an understanding of the chemical properties of ox-bridged binuclear iron centers. This study is intended to provide such an understanding. The ultimate objective of this project is to develop small, well-characterized model compounds which mimic the essential spectroscopic, structural, and functional features of the naturally occurring oxo-bridged diiron centers. Specific aims are to construct and characterize chemical analogues for the [Fe-III Fe-III] met, [Fe-II Fe-III] semi-met, and [Fe-II Fe-II] deoxy forms of hemerythrin. As such, flexible macrocyclic hexadentate and pentadentate nitrogenous ligands and congeners containing covalently appended carboxyl groups will be prepared. These ligands incorporate the essential coordination features characteristic of hemerythrin and are expected to stabilize binuclear iron complexes in a range of oxidation states. The iron-containing products prepared in this study will be characterized by a wide range of physical methods. This will be done both here at Austin and in collaboration with Pennsylvania State University and Stanford University. The chemical behavior of the synthetic diiron systems will be probed and careful comparisons to the natural systems will be made. This will provide specific information about hemerythrin and set the stage for developing reversible nonheme O-2 carriers.